This invention relates to elastomer compositions and to a method for making them. The blends comprise acrylic rubber and another elastomer which can be nitrile rubber, hydrogenated nitrile rubber, a fluoroelastomer, a silicone rubber or a fluorosilicone rubber. The elastomer compositions all have excellent resistance to the degrading effects of oil and heat.
It is known to blend different elastomers in an effort to obtain a combination of the beneficial properties of each; however, such blends often have properties which are, in fact, inferior to those of the components, because of incompatibility between different pairs of elastomers. Differences in viscosity in the unvulcanized state, in surface energy and in vulcanization rate can produce heterogeneous mixtures which are said to be "technologically incompatible." Thus, simple blends of two or more dissimilar elastomers often fail to achieve the desired combination of the good properties of each.
Elastomers which possess superior properties with regard to service temperature and low oil-swell are often referred to as "extreme-service" elastomers. Typical of these materials are fluorocarbon rubbers, fluorosilicone rubbers and silicone rubbers. A principal drawback of these materials is their high cost.
Other elastomers, such as nitrile rubber, have excellent oil-swell properties, but do not have high service temperatures. Still others, such as acrylic rubber, have fairly high service temperatures as well as very good oil resistance.
A desirable result, therefore, is a blend of elastomers which can produce a composition which has the properties of resistance to both heat and oil at a reasonable cost, yet is so produced as to minimize the technological incompatibility often associated with blends of dissimilar elastomers.